Casting method



- will appear as the description proceeds.

Patented it... 19, 1e45 Q UNITED STATES PATENT OFFICE- t 378,723,

John J. Nolan, .Ir., New York, N. Y., arch-nor. to The Central Foundry Company, New York, N. Y., a corporation of Maine No Drawing. Application August 3, 1943, Serial No. 497,223

' 4Ciaims- (01. 22-2005) The invention relates to the centrifugal casting of pipe and similar articles.

Centrifugal casting is today the accepted method for producing cast iron pipe of the type known as pressure pipe. In the United States, most'castiron pipe of'this type is manufactured in accordance with the DeLavaud centrifugal casting-process, which involves the use of rotatingwater-cooled molds. The pipe so cast,

as removed from the molds, has the characteristic hardened skin found in castings produced in permanent, or chill, molds. The structure of the metal in the skin of the casting is essentially that of white cast iron, having all of the carbon in combined form or in a pearlite-cementite microstructure without any appreciable amount of free graphite. Because of the hardness and brittleness of the skin it is the usual practice to anneal the pipe. This is an expensive, time-consuming operation. One of the leading objects of my invention is to provide a method of centrifugaliy casting iron pipe and similar articles in metal molds which will produce pipe that does not have to be annealed.

Second to the DeLavaud .process in commercial importance in this country is the method of casting in centrifugal molds provided with a sand or refractory lining. Pipe manufactured in this manner does not have to be annealed, but the process has many disadvantages as compared with centrifugal casting in permanent molds. Sand or refractory linings must constantly be renewed or replaced; which not only is an expensive operation in itself, but also delays production or necessitates providing a greater number of extra molds to permit renewing one set of molds while casting is being carried out in another. It is an object of my invention to provide a centrifugal casting method which will avoid the use of molds having sand or other refractory linings, yet which will produce gray iron pipe that does not have to be annealed after casting, thus overcoming the principal disadvantages of each of the two leading pipe casting processes in use at the present time.

Another object of the invention is to provide a centrifugalpipe casting method which is simpler and faster than any commerciallypracticable methodheretofore devised.

Other objects and advantages of my inventio In accordance with my invention the molten iron is introduced into a permanent mold, such as a two part iron mold, arranged to rotate at a suitable speed-around its longitudinal axis to distribute the iron arolind the periphery of the mold,

I and the casting is removed from the moldsubstantially at the moment that it has solidified sufllciently to hold its form. I have found that the time of removal of the casting from the mold is highly critical in its relation to the tempera ture of the casting, and that by proper control I of this critical factor it is actually possible to make what in effect is an unchilled casting in a mold which ordinarily is described as a permanent, or chill mold. I do not cool the mold with water as in the DeLavaud process and others; nor do I line the mold with sand or other molded refractory materials as proposed by those who seek an unhardened casting which does not have to be annealed. Yet I have actually produced unhardened castings in the so-called chill molds by the simple .but efiective expedient of selecting a type of mold which permits rapid removal of the casting and effecting such removal at the very moment that the casting has solidified sufflciently to hold its form.

I am'aware that two-part molds for centrifugal casting have been prosposed heretofore-although I know of none that has ever been found practicable. I am also aware that it has been proposed to cast'pipe in non-chilling molds, and that it has even been suggested thatit would be possible to so control cooling in a permanent mold as to produce a pipe which does not have to be annealed. I do not know that this desired result has ever been found possible of attainment. However, I have discovered that the real practical solutionof the problem lies, not in attempting to control cooling in the 'mold, but rather in controlling the time of removal of the casting from the mold. Thi solution'not only makes it thoroughly practicable to produce gray cast iron pipe in iron molds without annealing,

but results in speeding up the casting process itself. For example, I have found that in making a cast iron pipe'section 6.9 inches. in diameter and 5 feet long, weighing pounds, the entire casting operation can be performed in as little as 10 seconds, and the pipe can be on the cooling rack 25 seconds later, which includes the time for moving the mold to the opening station, opening it, lifting out thepipe and placing it on the fiuxing, substance is deposited in the mold. As

the mold rotates, this powdered substance is distributed more or less uniformly over the inner mold surface. When the powder is placed directly in the mold, the in-running metal washes it away at thqpointrthat the metal strikes the mold. To overcome this difficulty, I put a batch of powder in the end ofthe trough, and as the iron runs through the trough it pushes this batch ahead of it, distributing the powder as it goes. This powder may contain about per cent of carbon, preferably in the form of graphite, and about 85 er cent of inert," or, non-fiuxing .material, such as alumina, aluminum silicate, mag-. nesium oxide, magnesium silicate, or combinations thereof, alTpowders being of a grade of 100-200 mesh. While I prefer to use 15 per cent of carbon and 85 per cent of alumina or other inert material, this proportion may be varied somewhat. Under most conditions best results are to be had by using from about 10 per cent to about per cent of carbon.

The speed of rotation of the mold during pouring of the metal, preferably is about 700 R. P. M. The pouring operation, in the case of a '70 or 90 pound pipe requires approximately 3 seconds, thus rapidly distributing the iron for substantially instantaneous and simultaneous solidification throughout the mold. If desired, the speed of rotation during pouring of the metal may be lower-say 600 R. P. M. In this case it is preferable to increase the speed of rotation immediately following completion of the pouring operation-say to 800 R. P. M. As soon as the metal has solidified sufllciently to hold its form-about- 10 seconds after the beginning of the casting operation-the mold halves are separated and the casting quickly removed. I have found that if.

the casting is removed when it is at a temperature of between about 1500 Fahrenheit and about 2100 Fahrenheit, the resulting casting will have substantially all of the carbon in the form of pearlite and graphite so that annealing is unnecessary. The average and preferred temperature of the casting upon removal from the mold is about 1800* Fahrenheit. I make no attempt to control the mold temperature by heating or cooling, other than the heating which occurs by reason of the heat contained in the molten metal as cast. The 'mold may, in the first instance, be at room temperature, but thereafter it is not necessary "or :desirable to cool it down to room temperature again before a succeeding casting operation .is performed therein. Ordinarily, the mold temperature should not be appreciably higher than 800 Fahrenheit when the metal is cast.

The temperature of the iron as cast may vary from about 2500 Fahrenheit to 2550 Fahrenheit, although other suitable pouring temperatures may be availed of. This is not a feature of my present invention, and ismentioned simply in the interest of fullness of description.

After the castings have been placed on the cooling rack, they are allowed to cool slowly to produce a gray cast iron structure without annealing.

The terms and. expressions which I have employed are used in a descriptive and not a limiting sense, and I have no intention of excluding such equivalents of the invention described, or of portions thereof, as fall within the purview of the claims.

I claim:

1. The method of making annular gray cast iron objects which comprises introducing into an uninsulated metal mold molten iron capable of transforming into gray iron on slow cooling, rotating the mold about its longitudinal axis to rapidly distribute the iron in a thin layer around the periphery of the mold for substantially instantaneous and simultaneous solidification throughout the mold, and removin the casting from the mold substantially at the moment that the iron has solidified sufilciently to hold its form so as to produce'upon slow cooling a casting having substantially all of the carbon in the form of pearlite and graphite.

2. The method of making gray cast iron pipe in an uninsulated metal mold without subsequent annealing, comprising the steps of introducing molten iron capable, of transforming into gray iron on slow cooling into a rotating uninsulated metal mold to rapidly distribute the iron in a thin layer around the periphery of the mold for substantially instantaneous and simultaneous solidification throughout the mold, removing the casting from the mold substantially at the moment that the iron has solidified sufficiently to hold its form, and cooling the casting in air.

3. The method of making annular gray cast iron objects which comprises introducing molten iron capable of transforming into gray iron on slow cooling into an uninsulated split iron mold rotating at a suitable speed to rapidly distribute the iron in a thin layer around the periphery of the mold for substantially instantaneous and simultaneous solidification throughout the mold, opening the mold substantially at the moment that the iron has solidified sufficiently to hold its form and immediately thereafter removing the casting from the mold.

4. The method acording to claim 1 in which a powder consisting predominantly of a nonfiuxing material is introduced into the mold ahead of the molten iron.

' JOHN J. NOLAN, JR. 

